This invention relates generally to the construction of tanks or containers for granular or fluent particulate materials. More particularly, the invention relates to the construction of a trailer-mounted tank having at least one product compartment that is capable of being pressurized for discharge or unloading of the product therefrom.
Many granular or fluent particulate materials are conveniently transported by truck, although they may also be transported by railcar, barge or by other means. Trucks that are used to transport such materials may include a tractor and an attached trailer having a tank or other container mounted thereon. Frequently, these trailers are referred to as pneumatic tank trailers because of the pneumatic method, involving gas-or air-entrainment, by which they may be loaded and unloaded. Materials that are generally transported in pneumatic tank trailers include agricultural products such as grain, corn kernels, beans, flour, sugar, peanuts and the like, and intermediate products for various industrial uses such as plastic pellets, coke, lime, silica gel, powdered acid resins, rare earth powders and powdered alumina, and many others.
Pneumatic tank trailers include one or more product tanks or compartments which are generally enclosed by a sheet metal sheath. Because these pneumatic trailers are generally unloaded by a method which involves pressurizing the product compartments, the compartments are usually cylindrical or spherical in shape. Such shape also insures that the compartments can be easily and completely emptied. Each of the product compartments is provided with a discharge hopper that may be generally cylindrical or conical in shape, and the external sheath provides an aerodynamically efficient outer tank surface which may include end sections that are tapered.
One type of known construction of such pneumatic trailers includes a container comprised of a generally cylindrical and horizontally disposed upper central section to which are attached first and second conical ends. A lower central section is defined by one or more cylindrical or conical product compartments, the axes of which intersect the upper central section generally at right angles to the axis of the cylinder of the upper central section. The lower central section also includes an unloading system having a valve for each product compartment and a conduit extending from the valve to permit unloading of the compartment under pressure. The container is mounted on a frame which is supported by the chassis of a trailer.
The various components of the container are formed of metal sheets or panels which are welded together. The end sections are welded to the upper and lower central sections, and the upper and lower central sections are welded together. This construction of complex shapes resulting from the joining of the cylindrical upper central section and the cylindrical or conical lower central section creates stress risers in the container. In addition, welding of these various metal panels in the construction of the container changes the stiffness of the panels and creates additional stress risers. Furthermore, the construction of the conventional container includes several adjacent panels having welded joints that terminate at a common point. Because several welded joints are made close together in such construction, the area of each panel in the immediate vicinity of the common termination point of the welds is repeatedly subjected to the rapid heating to a high temperature that is an inevitable result of welding. Residual stresses or annealing effects from welding of these adjacent panels to a common termination point may affect their fatigue strength and buckling strength. Furthermore, the tensile or compressive strength of some joints may be reduced in the heat-affected zones adjoining the welds. Since the containers are subjected to cycles of pressurization and de-pressurization upon loading and unloading of product, and since the welded joints are subjected to fatigue caused by this cyclic loading and unloading of the product and also to vibrations caused by product transport, the joint in the heat-affected zone of each panel in the vicinity of the common weld termination point may fail after relatively few such cycles.
It would be desirable, therefore, if a construction technique could be developed for such containers that would minimize the creation or development of heat-induced fatigue in the panels which make up the container surface. It would also be desirable if such a construction technique could be developed that would permit the welding of adjacent panels having complex shapes while avoiding the placement of a plurality of welds in a relatively small area of the container surface.
Among the advantages of the invention is that it allows for the construction of efficiently shaped containers comprised of a plurality of panels in a manner that minimizes the creation or development of heat-affected zones and stress risers in the panels from welding. Another advantage of the invention is that it permits the welding of adjacent panels having complex shapes while avoiding the placement of a plurality of welds in a relatively small area of the container surface.
Additional objects and advantages of this invention will become apparent from an examination of the drawings and the ensuing description.
As used herein, the term xe2x80x9cgenerally cylindricalxe2x80x9d, as used to modify a component or components, refers to components comprised of cylinders having cross-sections that are wholly or partially cylindrical or elliptical, as well as polyhedral components such as those having cross-sections that are triangular, square, rectangular, hexagonal, octagonal, or of other similar shape.
As used herein, the term xe2x80x9cfatiguexe2x80x9d refers to the phenomenon leading to fracture under repeated or fluctuating stresses having a maximum value less than the tensile strength of the material. Fatigue fractures are progressive, beginning as minute cracks that grow under the action of the fluctuating stress.
As used herein, the term xe2x80x9cheat-induced fatiguexe2x80x9d refers to fatigue occurring in panels or other components that is caused by or contributed to by residual stresses or annealing effects from welding of such panels or components.
As used herein, the term xe2x80x9cweldingxe2x80x9d refers to the joining of two or more pieces of material by applying heat or pressure, or both, with or without filler material, to produce a localized union through fusion or recrystallization across the interface. A union made by welding is a weld.
The invention comprises an improvement in a method for constructing a container having at least three panels, all of which intersect at a common point and each adjacent pair of which intersect along a line. The improvement comprises: (a) welding each adjacent pair of panels to join them together by placing a weld along the intersecting line between such panels to a weld-terminating point spaced from the common intersecting point of the panels, (b) providing a patch component that is adapted to cover the common intersecting point and each weld-terminating point and to intersect with each panel along a line, and (c) welding the patch component to each of the panels by placing a weld along the line of intersection with each panel.
In order to facilitate an understanding of the invention, the preferred embodiments of the invention are illustrated in the drawings, and a detailed description thereof follows. It is not intended, however, that the invention be limited to the particular embodiments described or to use in connection with the apparatus illustrated herein. Various modifications and alternative embodiments such as would ordinarily occur to one skilled in the art to which the invention relates are also contemplated and included within the scope of the invention described and claimed herein.